I'm not quite sure on this, but I think a single 12MHZ clock 8052-based device won't be "strong" enough for that - Look for DSPs or think of connecting at least 2 microcontrollers (like, one to handle all "commands", "transmission", and all miscellaneous tasks and one as a dedicated realtime wave generator.)
I was (accidentially) generating some a high audio frequencies with an ADuC812 and an electric motor (motor speed set by dutycycle instead of DAC) but I think to generate good audio signal you'd need something faster.
-Maybe- 8051 clones that can run at seriously higher clock frequencies would suffice. Otherwise think DSP.